This disclosure relates to methods for validating qualitative and quantitative results of assessments of properties, fates and effects of substances and organs and/or tissues contacted by them, such as absorption, transport, metabolism, elimination, efficacy and/or toxicity of substances, such as chemical compounds and, particularly, drugs and drug candidates, when perfusing human-derived organs and/or tissues ex vivo with compatible perfusate solutions containing such substances. Methods of the invention permit validating results of such assessments using human-derived organs and/or tissues, particularly human organs and tissues unsuitable for transplantation, on an organ-by-organ or tissue-by-tissue basis.
Methodologies available for assessing substances and human organs and/or tissue affected by them span many levels of mammalian organization from in vivo studies to studies of isolated organs or tissues, tissue slices, cultured cell types, subcellular particles, multi-enzyme complexes and molecular interactions. In practice, these complex methods often result in considerable wasted time, effort and resources in many fields, particularly drug development, where drug candidates may undergo several rounds of safety and efficacy testing yet later testing or market experience reveals undesirable effects, sometimes with tragic consequences. For example, drugs that have been approved for human use but later recalled due to toxicity issues include COX-2 inhibitors, phexophenadine and thalidomide.
In early clinical trials, adverse benefit/risk ratios frequently cause the demise of otherwise promising pharmacologically active substances. Such events are costly and can have a profound effect on drug discovery, health care and industry stability. Historically, attempts to weed-out substances having an unacceptable benefit/risk ratio have relied on in vivo non-human animal studies using several species, such as rodent species. However, unlike inbred strains of animals used in drug development, the target species, i.e., humans, is, by comparison, very diverse in form and function. Thus, the quantitative and qualitative properties, fates and effects of substances, such as drug candidates and drugs, are also very diverse.
Limitations of toxicity studies in non-human species have long been, and still are, well recognized in the pharmaceutical industry, but short of performing toxicity studies in humans in vivo, there has been no viable alternative. As it is not ethical to use humans for exploratory toxicity testing, the choice has been to perform in vivo testing on a variety of non-human animal species and/or in vitro testing using human biological samples. Attempts have been made to bridge the gap between non-human testing results and effects in humans using tissue preparations containing subcellular particles, e.g., microsomes, primary cells and cells in culture, e.g., hepatocytes, and tissue slices. Although these in vitro tissue preparations generate much useful data, many drug candidates still fail in clinical trials because of adverse risk issues. There is ample evidence in the literature to suggest that this is due, at least in part, to the fact that the farther the tissue preparation is from the whole organism, the greater the risk of false positives and false negatives. For example, false positives or false negatives may occur when assessing whether test substances administered in therapeutic doses are toxic when administered alone or with other co-administered drugs. It is recognized that the confidence in the safety and efficacy of a drug compound increases as it moves from preclinical to clinical testing. It is also recognized, however, that the dangers of unforeseen deleterious results also increase. There is simply no guarantee that pharmacokinetic/toxicity relationships in normal human tissues determined in vitro will be the same as in diseased human tissues in vivo.
It is often difficult, if not impossible, to obtain samples from living human donors for drug development purposes. Unfortunately, samples from deceased donors have increased potential and actual levels of variability due to diseases and/or injuries that may or may not be related to the donor's death and/or due to variable levels of degradation after donation. Thus, it has been difficult to confidently generalize from data based on such human samples, especially at a level required for drug development. Furthermore, human samples have much more variability compared to samples from in-bred test animals.
U.S. Pat. No. 5,338,662 discloses methods for determining the effect of a test substance on an ex vivo organ. However, these methods rely on comparison to a simultaneously perfused control organ. While such methods may be suitable for organs of uniform nature and quality, such as organs from in-bred test animals, they do not account for the variability inherent in the use of human samples, especially from pre-deceased donors.
Thus, there is a need for improved methods for assessing and validating the results of assessments of substances that bridge the gap between in vivo non-human animal testing and human administration. There is a need for standardized validation testing of organs and tissues used to test substances, such as drug candidates. In addition, there is a need, in the drug development industry, for new and improved methods of validating the evaluation of potential drug candidates early in the research and development process, for providing reliable evaluations to drug development companies.